This article covers the topic in 7 sections: - Data Distribution Model
- ALE process
- IDOCS
- Converters
- Configuring ALE
- Other concepts
ALE Data Distribution Model
Data Distribution Model consists of all participating systems and the messages to be exchanged by the system.
Data Distribution in R/3 to R/3 environment is easily achieved, but in case of R/3 and non- R/3 systems we need to consider data mapping and other stuff.
The following figure illustrates the concept of data distribution using ALE.
Figure1: ALE Framework
Business objects of SAP are distributed with the help of BAPIs.
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BAPI’s – is a set of Interfaces to OO programming methods. Business Objects are held in BOR (Business Object Repository) which in turn encapsulate SAP data and process. External access to this data and process is only available through a method called BAPI. BAPI’s are implemented and stored in R/3 as Remote Function Call (RFC) modules.) While BAPI’s distributes the Business Objects, ALE acts as a layer that does the inter-linking of Business Objects at the application level. (like the name suggests, ALE, links the application layer)
ALE layer provides the following services:
- Application services: This layer is responsible for providing an interface (for instance: BAPI) to R/3 system to allow data exchange to or from external R/3 systems.
- Distribution Service: This layer is responsible for filtering and converting messages exchanged between SAP and Non-SAP systems. It is the core service, sandwiching between application and communication layers.
- Communication Service: This layer supports Synchronous and Asynchronous communication. (Sync messaging is used for direct reading of control data, while Async messaging is used to transmit and receive application data)
ALE Process
To understand the process flow, one must recognize the 3 primary entities which are involved in the message exchange process.
- SAP R/3 system
- ALE converter (inclusive of its sub-components)
- External non SAP R/3 system
The diagram below shows how they work together.
Figure2: ALE Functionality
Concept of Logical Systems (LS):
Logical system represents an R/3 system or an External system. The existence of LS is mandatory for the corresponding R/3 client (which uses ALE or EDI). One of the LS will be the ‘sender’ while the other will be ‘the receiver’.
In an Inbound ALE interface, the base LS will be the “Receiver” while the other LS will be the “Sender”.
Message Types:
Message types relate to the structure of the data called an IDOC (Intermediate Document). Message type provides the format of the data which can be exchanged between systems. ALE supports over 200 message types in R/3.
IDOCS
IDOCs are intermediate storage documents (of information) which allow data exchange between SAP R/3 system and Non-SAP system to take place. They are sent bi-directionally. Message types are responsible for creation of IDOCs.
IDOC Component and Structure
Just like in internet, where the data is exchanged using data formats like IPV6, here in SAP, IDOCs are used which are well-structured medium.
The figure below shows the component and the structure of an IDOC.
Figure 3: Component & Structure of IDOC
Components of IDOC:
- Control Record: Contains Control information of the IDOC being, the sender information, the receiver information, message type and IDOC type. Control Record is similar for all IDOC types.
- Data Segment: Contains the Header (identity of the doc) and data itself.
- Status Record: Shows the information regarding the already processed stages and to be processed stages of the IDOC. It has an identical format for each IDOC type.
Structure of IDOC:
IDOCs support a hierarchical structure. Figure 3 shows an IDOC, starting with the header. The header has items, which in turn have sub-items. The lowest level in the hierarchy contains the text. The end of the IDOC is represented with the help of ACCUM (means accumulate) segment. Remember that an IDOC can only contain character fields.
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